Motor vehicles such as automobiles, trucks, ambulances, and other emergency vehicles generally employ internal combustion engines which are liquid or fluid cooled. In cold climates, a portion of the engine coolant is continuously recirculated through a heat exchanger located to communicate with the interior of the vehicle. A fan is provided to recirculate air within the vehicle interior over the heat exchanger to warm the interior of the vehicle. While such a vehicle is in operation, heaters of this type provide ample warmth, even in the coldest of climates.
When a motor vehicle is parked with the engine turned off for a period of time in cold weather, such as overnight, the engine block, accessories, and the interior of the vehicle generally attain the ambient temperature surrounding the vehicle. It is common to encounter substantial difficulty in starting the engine of such a vehicle in cold weather. In addition, a considerable time period often is required before the engine coolant reaches a temperature which is sufficiently high to permit adequate heating of the vehicle interior through the recirculating coolant heater to take place. Other disadvantages include the frosting of the vehicle windshield and inefficient operation of the engine until it has attained its desirable operating temperature.
In the case of emergency vehicles, the problem of permitting the interior of the vehicle to reach the very cold ambient temperatures in which the vehicle may be parked in northern climates goes beyond the problems mentioned above. Ambulances and fire department rescue vehicles all include basic medical equipment which does not function properly when it is extremely cold. Particularly, if intravenous solutions of various types are kept in the vehicle, it is necessary to maintain a temperature within the vehcle above the freezing point of the solutions to prevent their deterioration or destruction.
Consequently, it has been common, in the case of ambulances or similar emergency vehhcles, to place an electric space heater within the vehicle whenever it is parked overnight or %for a long period of time and to connect the heater to a suitable source of household alternating power current. Space heaters are available in sizes sufficiently large to maintain the interior of such an emergency vehicle or ambulance at least above the freezing point, so that the intravenous solutions and other medical products stored within the ambulance are not permitted to freeze or be subjected to sub-freezing temperatures. When a call is received, however, to require the services of the emergency vehicle, it is necessary, as a first step when such a heater is being used, to either unplug the heater and store it somewhere within the vehicle or remove the heater from the vehicle before departing. The heater, however, does not overcome the difficulties inherent in starting the engine of such an emergency vehicle; so that all of the problems which occur in conjunction with extremely cold weather starting are present whether or not such a separate auxiliary electric space heater is used.
Various proposals have been made in the past for heating the vehicle interior, the engine, and/or charging the battery of a vehicle when it is parked for a relatively long period of time in sub-freezing temperatures. One such solution is disclosed in the patent to Edlund et al, U.S. Pat. No. 3,870,855, issued Mar. 11, 1975. The Edlund patent discloses a combination battery charger, motor heater, and passenger compartment heater for a motor vehicle. The passenger compartment heater is a separate resistance electric heater with its own heating fan. An engine heater (apparently in the form of an oil pan heating probe) also is provided, and a central unit is connected to the household alternating current line for supplying heating current to the engine heater, operating current to the air heater, and charging current to the vehicle battery. A problem with the system disclosed in the Edlund patent is that a separate heater and fan unit is required apart from the conventional automobile heater and fan. In addition, a separate electric engine heater is required and a main voltage cable necessarily is located within the vehicle interior extending from the control unit to the heating elements of the additional electric heater.
A number of proposals have been made in the past for automobile preheaters or quick heat boosters which employ auxiliary liquid or gas fuel supplies, or which utilize a portion of the gasoline normally used to power the internal combustion engine. A serious fire hazard exists when systems of this type are employed because of the additional fuel tanks and because of the use of open heating flames to produce the desired auxiliary heat. Examples of this type of system, which all require substantial modification of the vehicle in which they are used, are shown in the patents to Young, U.S. Pat. Nos. 3,131,864, Sunday, 3,072,176, Hardy, 3,690,549, and Cornell, 3,362,637.
Other attempts to speed-up the application of heat to the vehicle interior after the vehicle is started are disclosed in the patents to Wallace, U.S. Pat. No. 3,264,450 and Nilssen, 3,300,619, which employs auxiliary electric quick heat coils for an automobile. These coils are turned off after the engine heats up. There is no provision in the systems disclosed in either of these patents, however, for providing stand-by heat to the interior of the vehicle or to its engine. The auxiliary heaters are utilized only during the time period after the engine first is started until a satisfactory heat level is attained in the interior of the automobile.
Another system to provide auxiliary heat to the interior of an automobile is disclosed in the patent to Schott, U.S. Pat. No. 3,418,450. This patent discloses a car heater and battery charger using an alternating current resistence heater connected to an external alternating current power supply. A separate heater is necessary in addition to the normal hot water heater which is standard in most vehicles.
Other systems have been proposed for providing a centralized boiler or heat source with auxiliary equipment in buses, or the like, to connect to the centralized heat source for maintaining an elevated interior temperature in the buses or similar vehicles during times when they are parked in cold weather.
It is desirable to provide auxiliary heater and power supply systems particularly suitable for use with ambulances and similar emergency vehicles for maintaining interior heat in the vehicle along elevating the temperature of the engine coolant and providing auxiliary electrical power for vehicle accessories, if desired, without being subject to the various disadvantages of the prior art discussed above.